1. Field of Invention
This invention relates to means for reducing the polution in internal combustion engines and more particularly to means for controlling the secondary air injected in an internal combustion engine pollution control system.
2. Description of the Prior Art
To control the pollution of an internal combustion engine, it is frequently necessary to provide a secondary air injection system designed to promote the combustion of the unburned components of the exhaust gas by means of the injection of secondary air into a conventional exhaust system. Such prior art systems typically include a secondary air to fuel ratio sensor in the exhaust system for determining the concentration of oxygen or the concentration of carbon monoxide in the exhaust gas. When the output of this air to fuel ratio sensor varies from a given value, a control valve is regulated by a control circuit which sends out a signal so that the amount of secondary air is increased. The secondary air to fuel ratio of the exhaust gas is established at a theoretical mixture ratio (air excess rate .lambda. equals 1), and a catalytic agent or reactor is used to activate combustion.
However, although it is necessary to increase the amount of secondary air injected when the amount of exhaust gas is abruptly increased due to a sudden acceleration of the vehicle and particularly when the amount of gas is increased immediately after shifting gears in automobiles with manual transmissions, the prior art feedback controlled secondary air injection systems for supplying secondary air are not able to keep up with the increase in the amount of exhaust gases. Accordingly, these prior art systems have suffered from a drawback of allowing the emission of large amounts of unburned components of the exhaust gas into the atmosphere due to insufficient combustion of the components (particularly the recombustion of carbon monoxide).
This invention has been designed to eliminate the above mentioned prior art drawback.